A new nanoscale view of the biological world

With the mult-isotipe imaging mass spectrometry (MIMS) Doctors might soon be able to track individual donor cells after a transplant, or to find where and how much of a cancer treatment drug there is within a cell. "This method allows us to see what has never been seen before, and to measure what has never before been measured," Claude Lechene of Harvard Medical School says.

"Imagine looking into a building, slice by slice. You can see not only that it contains apartments, but also that each apartment contains a refrigerator. You can see that there are tomatoes in the refrigerator of one apartment, and potatoes in the refrigerator of another. It is this level of resolution and quantification that MIMS makes possible within cells."

A beam of ions is used to bombard the surface atoms of the biological sample, and a fraction of the atoms are emitted and ionized. These "secondary ions" can then be manipulated with ion optics – in the way lenses and prisms manipulate visible light - to create an atomic mass image of the sample.

MIMS can generate quantitative, three-dimensional images of proteins, DNA, RNA, sugar and fatty acids at a subcellular level in tissue sections or cells. "Using MIMS, we can image and quantify the fate of these molecules when they go into cells, where they go, and how quickly they are replaced," says Lechene.

The method does not need staining or use of radioactive labelling. Instead, it is possible to use stable isotopes to track molecules. For example, researchers could track stem cells by labelling DNA with 15N. "These stable isotopes do not alter the DNA and are not toxic to people; with MIMS and stable isotope labelling we could track these cells, where they are and how they have changed several years later," says Lechene.